1. Field of the Invention
The present invention relates to a pivotal connection or joint device for two members of an artificial joint intended to be attached to respective members for securing the artificial joint to the human body, comprising two supporting side plates fixedly associated with one another and parallel to one another, two pivot pins disposed between these side plates, two semi-circular toothed sectors mounted co-axially on the respective pivot pins, in contact with one another and fixedly associated with the respective members, and adjustable stop means extending into the path of at least one of these members to define its sector of freedom.
Artificial knee joints comprise means of fixation above and below the knee connected to two pivotal connection devices situated on the internal and external parts of the knee.
2. Description of the Prior Art
As is known, the bending-extending movement of the pivotal knee joint occurs by rolling and sliding of the femoral condyles on the articular discs of the tibial plate and not about a fixed center of rotation. This is the reason for the members connecting the fixation members of the artificial joint to the human body not generally being pivoted about a common axis, but about two parallel axes. The two members associated with the same pivotal connection device are kinematically connected, for example by two geared sectors in contact with one another. It is also known to define a sector of freedom for these members by disposing stops in their paths as a function of the bending-extending movement for which limitation of pivoting to that to which the pivotal joint is set is required. This choice is determined by the doctor who must himself carry out on the artificial joint the adjustment of the stops in the paths of the members of the pivotal connection device of the artificial joint.
There exist for this purpose different adjustment systems which have the disadvantage of necessitating tools such as screwdrivers in particular and dismantling and assembly operations with which the doctor is less familiar than the orthopedist.
In particular, there has been proposed in U.S. Pat. No. 4,817,588 such an adjustment system in which the stop members are positioned in notches spaced angularly about the axis of pivoting of an artificial joint, a locking member serving to retain these stop elements in their respective notches. The disadvantage of this adjustment system resides essentially in the fact that it is relatively complex and necessitates therefore the manufacture of quite a large number of components, leading to assembly operations the duration and the difficulty of which are a function of the number of pieces to be put together.
European Patent Specification No. 0,059,472 and U.S. Pat. No. 4,726,361 describe a simpler adjustment system comprising stops disposed along arcuate grooves centered on axes of pivoting and located along these grooves by being secured in position using a screw and a nut disposed one to each side of the plane of the plate in which the groove is formed. The disadvantage of a system of this kind is that the angular position is only defined by the grip of the stops. Taking account of the force which these stops are called upon to withstand by virtue of the length of the arm of the lever, the position of these stops may be accidentally changed.
Another solution proposed in U.S. Pat. No. 4,493,316 comprises two gear wheels carried by arms secured on the axes of pivoting of the two members of the artificial joint, each of which is in engagement with a gear toothing integral with one of these axes, so that these gear wheels are displaced in an angular sense with these gear toothings and limit the angular displacement when they meet the other integral gear toothing of the axis of pivoting of the other member of the artificial Joint. This solution does not enable fixed positions to be determined, these always being a function of a securing operation and thus susceptible to being accidentally displaced.
The same disadvantage is found in British Patent Specification No. 2,182,714A, the angular displacements of the members of the artificial joint being limited by stop screws capable of being dislocated.
As may be confirmed, there does not exist in the state of the art a simple adjustment device capable of defining angles of pivoting in a manner which is incapable of maladjustment, that is to say stop positions which are not dependent upon a simple gripping force. In addition, all of these devices require a specific set of tools not normally available to a medical practitioner.